Read-assist circuits for memory bit cells employing a p-type field-effect transistor (pfet) read port(s), and related memory systems and methods

ABSTRACT

Read-assist circuits for memory bit cells employing a P-type Field-Effect Transistor (PFET) read port(s) are disclosed. Related memory systems and methods are also disclosed. It has been observed that as node technology is scaled down in size, PFET drive current (i.e., drive strength) exceeds N-type FET (NFET) drive current for like-dimensioned FETs. In this regard, in one aspect, it is desired to provide memory bit cells having PFET read ports, as opposed to NFET read ports, to increase memory read times to the memory bit cells, and thus improve memory read performance. To mitigate or avoid a read disturb condition that could otherwise occur when reading the memory bit cell, read-assist circuits are provided for memory bit cells having PFET read ports.

PRIORITY APPLICATION

The present application is a divisional application of and claimspriority to U.S. patent application Ser. No. 14/862,712 filed on Sep.23, 2015 and entitled “READ-ASSIST CIRCUITS FOR MEMORY BIT CELLSEMPLOYING A P-TYPE FIELD-EFFECT TRANSISTOR (PFET) READ PORT(S), ANDRELATED MEMORY SYSTEMS AND METHODS,” which claims priority under 35U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No.62/119,756 filed on Feb. 23, 2015 and entitled “READ-ASSIST CIRCUITS FORMEMORY BIT CELLS EMPLOYING A P-TYPE FIELD-EFFECT TRANSISTOR (PFET) READPORT(S), AND RELATED MEMORY SYSTEMS AND METHODS,” both of which areincorporated herein by reference in their entireties.

BACKGROUND I. Field of the Disclosure

The technology of the disclosure relates generally to memory systemsemploying addressable static memory bit cells for reading and writingdata, and more particularly to read-assist circuits for mitigating readdisturb conditions when reading from bit cells.

II. Background

Supply voltage (i.e., Vdd) scaling is an effective technique formaximizing processor energy efficiency across all market segments,ranging from small, embedded cores in a system-on-a-chip (SoC) to largemulticore servers. As supply voltage in processor-based systems isreduced to conserve power, circuit delay sensitivity to parametervariations amplifies, eventually resulting in circuit failures. Thesecircuit failures limit the minimum operating supply voltage and themaximum energy efficiency of processor-based systems. In currentprocessor-based system designs, static random-access memory (SRAM)caches and/or register files limit the minimum operation supply voltage.SRAM cache and register file bit cells employ near minimum-sizedtransistors to maximize capacity. Since uncorrelated parametervariations (e.g., random-dopant fluctuations, line-edge roughness) areinversely proportional to the square-root of the transistor gate area,wide differences exist for the memory bit cell minimum operating voltageto read, write, and retain data.

In this regard, FIG. 1 is a schematic diagram of an exemplary SRAMsystem 100 employing memory bit cells 102(0)(0)-102(M)(N) (“bit cells102(0)(0)-102(M)(N)) for storing data in a data array 104. The dataarray 104 is organized as having ‘M+1’ bit cell columns and ‘N+1’ bitcell rows of bit cells 102 supporting an “N+1” bit wide data word. Abitline driver 112(0)-112(N) is provided for each bit cell column 0-N todrive a selected bitline 114(0)-114(N) and a complement bitline(bitline_b) 114′(0)-114′(N) for read and write operations. A wordlinedriver 108(0)-108(M) is provided for each bit cell row 0-M in the dataarray 104 to control access to the addressed bit cells 102( )(0)-102()(N) in a given bit cell row 0-M based on an index(0)-index(M) decodedfrom a memory address indicating the bit cell row 0-M to be selected. Aclock signal (clk) 110 controls the timing of asserting the activatedwordline 106(0)-106(M) to access a row of bit cells 102( )(0)-102( )(N)in the selected bit cell row 0-M. The wordline driver 108(0)-108(M) forthe selected bit cell row 0-M causes the data stored in the selected bitcells 102( )(0)-102( )(N) to be asserted onto the bitlines 114(0)-114(N)and complement bitlines 114′(0)-114′(N) to be sensed by sense amplifiers116(0)-116(N) provided in each bit cell column 0-N. The sense amplifiers116(0)-116(N) provide the data bits from the selected bit cells 102()(0)-102( )(N) onto respective data output lines 118(0)-118(N).

FIG. 2 is a circuit diagram of a bit cell 102 in the SRAM system 100 inFIG. 1. In this example, the bit cell 102 is a standard six (6)transistor (6-T) static complement memory bit cell. The bit cell 102comprises two (2) cross-coupled inverters 120(0), 120(1) powered byvoltage Vdd. The cross-coupled inverters 120(0), 120(1) reinforce eachother to retain data in the form of a voltage on a respective truestorage node (T) 122 and a complement storage node (C) 122′. Eachinverter 120(0), 120(1) is comprised of a respective pull-up P-typefield-effect transistor (PFET) 124(0), 124(1) coupled in series to arespective pull-down N-type field-effect transistor (NFET) 126(0),126(1). NFET access transistors 128(0), 128(1) are coupled to therespective inverters 120(0), 120(1) to provide respective read/writeports 130(0), 130(1) to the bit cell 102. In a read operation, thebitline 114 and complement bitline 114′ are pre-charged to voltage Vdd.Then, the wordline 106 coupled to gates (G) of the NFET accesstransistors 128(0), 128(1) is asserted to evaluate the differentialvoltages on the true storage node 122 and complement node 122′ to readthe bit cell 102. If a logic high voltage level (i.e., a ‘1’) is storedat the true storage node 122 (T=1) and a logic low voltage level (i.e.,‘0’) is stored at the complement storage node 122′ (C=0), assertion ofthe wordline 106 will cause the NFET access transistor 128(1) todischarge the pre-charged voltage on the complement bitline 114′ to thecomplement storage node 122′ and through the NFET 126(1) to ground.However, if the NFET access transistor 128(1) is a faster device thanthe PFET 124(1), the discharge of the pre-charged voltage on thecomplement bitline 114′ can cause a charge build up on complementstorage node 122′ that can cause inverter 120(0) to flip the voltage onthe true storage node 122 from a logic ‘1’ to a logic ‘0’, which maycause a subsequent read operation to the bit cell 102 to returnerroneous data. This is known as a read disturb condition.

To mitigate or avoid a read disturb condition from occurring in the bitcell 102 in FIG. 2, the NFET access transistors 128(0), 128(1) could beweakened and the PFETs 124(0), 124(1) in the inverters 120(0), 120(1) bestrengthened. However, this can cause write contention issues in the bitcell 102. FIG. 3 is a circuit diagram illustrating a write contentionbetween the NFET access transistor 128(0) and the PFET 124(0) in theinverter 120(0) in the bit cell 102 in FIG. 2. For example, during awrite operation, if a logic ‘1’ is stored in the true storage node 122(T=1) (and a logic ‘0’ is stored in the complement storage node 122′(C−0)) and the data placed on the bitline 114 to be written to the truestorage node 122 is a logic ‘0’, the NFET access transistor 128(0)discharges the true storage node 122 to the bitline 114 to write a logic‘0’ to the true storage node 122. The NFET access transistor 128(0) iscapable of passing a strong logic ‘0’. However, the logic ‘0’ stored inthe complement storage node 122′ can cause the strengthened PFET 124(0)to overcome the drive strength of the NFET access transistor 128(0) tocharge the true storage node 122 to voltage Vdd (i.e., a logic ‘1’),thus causing a write contention on the true storage node 122.

SUMMARY OF THE DISCLOSURE

Aspects of the disclosure involve read-assist circuits for memory bitcells (“bit cells”) employing a P-type field-effect transistor (PFET)read port(s). Related methods and systems are also disclosed. The memorybit cells are provided in a data array of a memory system in aprocessor-based system to store data. It has been observed that as nodetechnology is scaled down in size, PFET drive current (i.e., drivestrength) exceeds N-type field-effect transistor (NFET) drive currentfor like-dimensioned FETs. This is due to the introduction of strainedsilicon in FET fabrication to reduce the effective mass of chargecarriers. The read port is a performance critical element in a memorybit cell. In this regard, in one aspect, it is desired to provide memorybit cells having PFET read ports, as opposed to NFET read ports, toreduce memory read times to the memory bit cells, and thus improvememory read performance. To mitigate or avoid a read disturb conditionthat could otherwise occur when reading the memory bit cell, read-assistcircuits are provided for memory bit cells having PFET read ports tomitigate a read disturb condition that could otherwise occur whenreading the memory bit cells. By mitigating or avoiding read disturbconditions in the memory bit cells, the voltage supply providing theminimum voltage to the memory bit cells for operation and data retentioncan be reduced to reduce power consumption and increase processor energyefficiency.

In this regard, in one aspect, a memory system is provided. The memorysystem comprises a memory bit cell. The memory bit cell comprises astorage circuit configured to store data. The memory bit cell alsocomprises one or more PFET access transistors coupled to the storagecircuit. Each of the one or more PFET access transistors comprises agate configured to be activated by a wordline in response to a readoperation to cause the one or more PFET access transistors to pass thedata from the storage circuit to a bitline read-assist circuit coupledto the memory bit cell. The memory system also comprises a read-assistcircuit configured to boost a voltage in the memory bit cell in responseto the read operation to assist in transferring the data from thestorage circuit to a bitline.

In another aspect, a method of reading data from a memory bit cell isprovided. The method comprises pre-discharging at least one bitlinecoupled to an access node of one or more PFET access transistors in amemory bit cell in response to a read operation. The method alsocomprises activating a wordline coupled to a gate of the one or morePFET access transistors in response to the read operation to transferdata from a storage circuit to the access node and the at least onebitline. The method also comprises boosting a voltage in the memory bitcell in response to the read operation to assist in transferring thedata from the storage circuit to the access node.

In another aspect, a non-transitory computer-readable medium havingstored thereon computer data for a library cell for an integratedcircuit (IC). The library cell comprises a memory system that comprisesa memory bit cell. The memory bit cell comprises a storage circuitconfigured to store data. The memory bit cell also comprises one or morePFET access transistors coupled to the storage circuit. Each of the oneor more PFET access transistors comprises a gate configured to beactivated by a wordline in response to a read operation to cause the oneor more PFET access transistors to pass the data from the storagecircuit to a bitline read-assist circuit coupled to the memory bit cell.The memory system also comprises a read-assist circuit configured toboost a voltage in the memory bit cell in response to the read operationto assist in transferring the data from the storage circuit to abitline.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of an exemplary processor-based memorysystem employing a static random access memory (SRAM) system comprisinga data array of static memory bit cells organized in rows and columnsfor storing data;

FIG. 2 is a circuit diagram illustrating a read disturb condition in astandard six (6) transistor (6-T) static complement memory bit cell thatcan be employed in the data array in the SRAM system in FIG. 1;

FIG. 3 is a circuit diagram illustrating a write contention between anN-type field-effect transistor (NFET) access transistor and an inverterP-type field-effect transistor (PFET) in a standard 6-T staticcomplement memory bit cell that can be employed in the data array in theSRAM system in FIG. 1;

FIG. 4 is a graph illustrating relative saturation drain currents(I_(DSAT)) of NFET and PFET technology as a function of technology nodesize;

FIG. 5 is a schematic diagram of an exemplary processor-based memorysystem employing an SRAM system comprising a data array of static memorybit cells employing a PFET read port;

FIG. 6A is a circuit diagram illustrating an exemplary avoidance of aread disturb condition in a standard 6-T static complement memory bitcell employing a PFET read port in the data array in the SRAM system inFIG. 5;

FIG. 6B is a flowchart illustrating exemplary processes providing readassistance for a memory bit cell including PFET access transistors inFIG. 6A to avoid or reduce read disturb conditions in the memory bitcell in response to a read operation;

FIG. 7 illustrates an exemplary read-assist circuit that includes anexemplary positive wordline boost circuit provided in a wordline driverto positively boost a wordline of the memory bit cell in FIG. 5 toweaken PFET access transistors in the memory bit cell in response to aread operation to mitigate or avoid a read disturb condition;

FIG. 8 illustrates an another exemplary read-assist circuit thatincludes another exemplary positive wordline boost circuit provided in awordline driver to programmably positively boost a wordline of thememory bit cell in FIG. 5 to weaken PFET access transistors in the bitcells in response to a read operation to mitigate or avoid a readdisturb condition;

FIG. 9 illustrates an another exemplary read-assist circuit thatincludes another exemplary positive wordline boost circuit provided in awordline driver to positively boost a wordline of the memory bit cell inFIG. 5 based on a different voltage supply than used for driving thewordline during write operations, to weaken PFET access transistors inthe memory bit cell in response to a read operation to mitigate or avoida read disturb condition;

FIG. 10 illustrates an another exemplary read-assist circuit thatincludes another exemplary positive wordline boost circuit provided in awordline driver to positively boost a wordline of the memory bit cell inFIG. 5 based on a different voltage supply than used for driving thewordline during write operations, to weaken PFET access transistors inthe memory bit cell in response to a read operation to mitigate or avoida read disturb condition;

FIG. 11 illustrates an exemplary read-assist circuit that includes anexemplary positive bitline boost circuit provided in a bitline driver topositively boost bitlines of the memory bit cell in FIG. 5 to weakenPFET access transistors in the memory bit cell in response to a readoperation to mitigate or avoid a read disturb condition;

FIG. 12 illustrates an exemplary read-assist circuit that includes anpositive supply rail positive boost circuit configured to positivelyboost a positive supply rail in a PFET(s) in a cross-coupled inverterstorage circuit in the memory bit cell in FIG. 5, to strengthen thePFETs in the storage circuit to be stronger than PFET access transistorsin the memory bit cell in response to a read operation to mitigate oravoid a read disturb condition; and

FIG. 13 is a block diagram of an exemplary processor-based system thatcan include memory systems that employ read-assist circuits for memorybit cells employing PFET read ports, and according to any of the aspectsdisclosed herein.

DETAILED DESCRIPTION

With reference now to the drawing figures, several exemplary aspects ofthe present disclosure are described. The word “exemplary” is usedherein to mean “serving as an example, instance, or illustration.” Anyaspect described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other aspects.

Memory bit cells are provided in a data array of a memory system in aprocessor-based system to store data. As shown in a graph 400 in FIG. 4,it has been observed that as node technology is scaled down in size,PFET drive current (i.e., drive strength) exceeds N-type field-effecttransistor (NFET) drive current for like-dimensioned FETs. This is dueto the introduction of strained silicon in FET fabrication to reduce theeffective mass of charge carriers. As illustrated in FIG. 4, thetechnology node size in nanometers (nm) is provided on an X-axis 402.The ratio of a saturation drain current (I_(DSAT, N)) of an NFET to thesaturation drain current of a PFET (I_(DSAT, N)/D_(SAT, P)) is providedon a Y-axis 404. The ratio of I_(DSAT, N) to I_(DSAT, P) as a functionof technology node size in nm is shown on a ratio line 406. As shown bythe ratio line 406 in FIG. 4, a PFET drive strength increases ascompared to a like-dimensioned NFET as the technology node sizedecreases. At point 408, the ratio line 406 crosses a ratio of 1.0 ofNFET drive current to PFET drive strength. Thus, in this example, thedrive strength of the PFET is greater than the drive strength of alike-dimensioned NFET.

In this regard, as discussed in more detail below, aspects disclosedherein involve read-assist circuits for memory bit cells employing aP-type field-effect transistor (PFET) read port(s). A read port may be aperformance critical element in a memory bit cell. In this regard, inone aspect, it is desired to provide memory bit cells having PFET readports, as opposed to NFET read ports, to decrease memory read times tothe memory bit cells, and thus improve memory read performance As shownin the saturation drive current (I_(DSAT)) equation below, an increasein the charge carrier effective mobility results in an increase in drivecurrent (I_(D)).

I _(D)=½μC _(ox) W/L(V _(GS) −V _(TH))²

where:

-   -   ‘μ’ is the charge carrier effective mobility,    -   ‘W’ is the gate width,    -   ‘L’ is the gate length,    -   ‘C_(ox)’ is the capacitance of the oxide layer;    -   ‘V_(GS)’ is the gate to source Voltage, and    -   ‘V_(TH)’ is the threshold voltage.

In this regard, in one aspect, it is desirable to provide memory bitcells having PFET write ports, as opposed to NFET write ports, to reducememory read times to the memory bit cells, and thus improve memoryperformance. To mitigate or avoid a read disturb condition that couldotherwise occur when reading the memory bit cell, read-assist circuitsare provided for memory bit cells having PFET read ports. By mitigatingor avoiding read disturb conditions in the memory bit cells, the voltagesupply providing the minimum voltage to the memory bit cells foroperation and data retention can be reduced to reduce power consumptionand increase processor energy efficiency.

In this regard, FIG. 5 is a schematic diagram of an exemplary SRAMsystem 500 employing PFET read port memory bit cells 502(0)(0)-502(M)(N)(also referred to herein as “memory bit cells 502(0)(0)-502(M)(N)”).PFET read port memory bit cells 502 are memory bit cells that each haveone or more PFET read ports. As discussed above, if the technology nodeof the memory bit cells 502(0)(0)-502(M)(N) is scaled down far enough,the memory bit cells 502(0)(0)-502(M)(N) will perform read operationsfaster than similar memory bit cells employing NFET read ports. Thememory bit cells 502(0)(0)-502(M)(N) are configured to store data in adata array 504. As a non-limiting example, the memory bit cells502(0)(0)-502(M)(N) may be standard six (6) transistor (6-T) or eight(8) transistor (8-T) static complement memory bit cells. The data array504 is organized as having ‘M+1’ bit cell columns and ‘N+1’ bit cellrows of memory bit cells 502 supporting an “N+1” bit wide data word. Forany given bit cell row 0-M in the data array 504, each bit cell column0-N of the data array 504 includes a memory bit cell 502 in which asingle data value or bit is stored.

With continuing reference to FIG. 5, write operations to the memory bitcells 502(0)(0)-502(M)(N) are controlled by respective wordlines506(0)-506(M) corresponding to each bit cell row 0-M. A read operationis performed on the memory bit cells 502( )(0)-502( )(N) in a given bitcell row 0-M based on an index(0)-index(M) generated as a result ofdecoding a memory address in a memory read operation indicating the bitcell row 0-M to be read. A wordline driver 508(0)-508(M) is provided foreach bit cell row 0-M in the data array 504 to control reading to theaddressed memory bit cells 502( )(0)-502( )(N) in a given bit cell row0-M based on the received respective index(0)-index(M). Thus, only onewordline driver 508(0)-508(M) is activated at a time in this example. Aread clock signal (read_clk) 510 controls the timing of asserting theactivated wordline (WL) 506(0)-506(M) to read the memory bit cells 502()(0)-502(0)(N) in the selected bit cell row 0-M.

With continuing reference to FIG. 5, a bitline driver 512(0)-512(N) isprovided for each bit cell column 0-N in the SRAM system 500 for readingdata from memory bit cells 502( )(0)-502( )(N) in the selected bit cellrow 0-M. In this regard, the bitline drivers 512(0)-512(N) drive abitline 514(0)-514(N) and a complement bitline (bitline_b)514′(0)-514′(N), because the memory bit cells 502(0)(0)-502(M)(N) employa complement bitline architecture.

In a write operation, data bits 0-N to be written are provided torespective bitline drivers 512(0)-512(N) to drive the received data bits0-N and their complement data bits onto the bitlines 514(0)-514(N) andcomplement bitlines 514′(0)-514′(N), respectively. The wordline driver508(0)-508(M) for the selected bit cell row 0-M is activated to selectthe memory bit cells 502( )(0)-502( )(N) to be written. The data bits0-N asserted on the bitlines 514(0)-514(N) and complement bitlines514′(0)-514′(N), respectively, are written into the selected memory bitcells 502( )(0)-502( )(N).

In a read operation, the bitline drivers 512(0)-512(N) pre-discharge thebitlines 514(0)-514(N) and complement bitlines 514′(0)-514′(N) during apre-discharge stage. The wordline driver 508(0)-508(M) for the selectedbit cell row 0-M causes the data stored in the selected memory bit cells502( )(0)-502( )(N) to be asserted onto the bitlines 514(0)-514(N) andcomplement bitlines 514′(0)-514′(N) to be sensed by sense amplifiers516(0)-516(N) provided in each bit cell column 0-N. The sense amplifiers516(0)-516(N) provide the data bits from the selected memory bit cells502( )(0)-502( )(N) onto respective data output lines 518(0)-518(N).

FIG. 6A is a circuit diagram illustrating how to avoid a read disturbcondition in a PFET read port memory bit cell 502 employing a PFETread/write port in the data array 504 in the SRAM system 500 in FIG. 5.FIG. 6B is a flowchart illustrating an exemplary process 600 foravoiding read disturb conditions in the storage circuit 501 in responseto a read operation. The process 600 in FIG. 6B will be discussed onconjunction with FIG. 6A.

With reference to FIG. 6A, the PFET read port memory bit cell 502comprises a storage circuit 501 in this example comprised of two (2)cross-coupled inverters 520(0), 520(1) powered by voltage Vdd. A truestorage node (T) 522 and a complement storage node (C) 522′ retain data532 (i.e., a charge) and complement data 532′ (i.e, a complement chargeto the data 532), respectively, in the form of voltages on therespective true storage node (T) 522 and the complement storage node (C)522′. Each inverter 520(0), 520(1) is comprised of a respective pull-upPFET 524(0), 524(1) coupled in series to a respective pull-down NFETs526(0), 526(1). Instead of providing NFET access transistors, PFETaccess transistors 528(0), 528(1) are coupled to the respectiveinverters 520(0), 520(1) to provide respective PFET read ports 530(0),530(1) to the PFET read port memory bit cell 502.

In this regard, in a read operation, the bitline 514 and complementbitline 514′ are pre-discharged to a low voltage (e.g., GND voltage)(block 602 in FIG. 6B). Then, the wordline (WL) 506 coupled to gates (G)of the PFET access transistors 528(0), 528(1) is activated or assertedto evaluate the differential voltages on the true storage node 522 andcomplement node 522′ to determine the stage of the data 532 andcomplement data 532′ stored in the storage circuit 501 of the memory bitcell 502 (block 604 in FIG. 6B). For example, FIG. 6A illustrates alogic high voltage level (i.e., a ‘1’) is stored at the true storagenode 522 (T=1) and a logic low voltage level (i.e., ‘0’) stored atcomplement storage node 522′ (C=0). The PFET 524(0) maintains the chargeon the true storage node 522. Assertion of a low voltage (e.g., GNDvoltage) on the wordline (WL) 506 after floating the bitline 514 and thecomplement bitline 514′ to read the memory bit cell 502 will cause thePFET access transistor 528(0) to charge the voltage on the bitline 514(i.e., charge the bitline 514). Similarly, assertion of a low voltage(e.g., GND voltage) on the wordline (WL) 506 to read the memory bit cell502 will not charge the complement bitline 514′ since the voltage on thecomplement bitline 514′ was pre-discharged to a low voltage (e.g, GNDvoltage) and the voltage at the complement storage node (C) 522′ is alsothe low voltage.

However, if the PFET 524(0) has a weak drive strength and is thus aslower device relative to a similarly sized NFET, as the bitline 514 isbeing charged by the PFET access transistor 528(0), the PFET 524(0) maynot have enough drive strength to quickly re-charge any lost charge onthe true storage node 522 as the voltage of the data 532 at the truestorage node 522 is coupled to the bitline 514. This loss of charge dueto charge sharing at the true storage node 522 can cause inverter 520(1)to flip the voltage on the complement storage node 522′ from a logic ‘0’to a logic ‘1’, which may cause a subsequent read operation to thememory bit cell 502 to return erroneous data. This is known as a readdisturb condition. This read disturb condition can limit the minimumsupply voltage for reading the memory bit cell 502 employing PFET readports 530(0), 530(1).

To mitigate or avoid a read disturb condition from occurring in thememory bit cell 502 in FIG. 6A, the PFET access transistors 528(0),528(1) could be weakened to decrease their gate (G) voltage-to-source(S) voltage (Vgs) voltages and/or the pull-down PFETs 524(0), 524(1) inthe inverters 520(0), 520(1) could be strengthened (block 606 in FIG.6B). In this regard, read-assist circuits can be provided to boost avoltage in the memory bit cell 502 in the SRAM system 500 in FIG. 5 toassist in transferring data 532 and/or complement data 532′ from thestorage circuit 501 to the respective bitline 514 and complement bitline514′ (block 606 in FIG. 6B). There are different exemplary read-assistcircuits disclosed herein that can be provided for the memory bit cell502 to mitigate or avoid read disturb contentions in response to readoperations. In this manner, as technology node size of the memory bitcell 502 is scaled down, the benefit of the faster read times in thememory bit cell 502 employing the PFET read ports 530(0), 530(1) can berealized while mitigating or avoiding read disturb conditions. Bymitigating or avoiding read disturb conditions in the memory bit cell502, the voltage supply providing the minimum voltage (Vdd) to thememory bit cell 502 for operation and data retention can be reduced toreduce power consumption in the SRAM system 500.

In this regard, as an example to mitigate or avoid read disturbconditions in the PFET write port memory bit cell 502 in FIG. 6A, aread-assist circuit employing a positive wordline boost circuitconfigured to positively boost the voltage of the wordline (WL) 506 inresponse to a read operation on the PFET read port memory bit cell 502can be employed (block 606A in FIG. 6B). Examples of memory systems thatinclude read-assist circuits employing positive wordline boost circuitsfor a PFET write port memory bit cell are shown in FIGS. 7-10, discussedbelow.

Also, as another example to mitigate or avoid read disturb conditions inthe PFET write port memory bit cell 502 in FIG. 6A, a read-assistcircuit employing a bitline positive boost circuit can be employed. Thebitline positive boost circuit is configured to positively boost thevoltage of a bitline coupled to the PFET write port memory bit cell 502in response to a read operation (block 606B in FIG. 6B). Examples ofmemory systems that include read-assist circuits employing a bitlinepositive boost circuit for a PFET write port memory bit cell are shownin FIG. 11 discussed below.

Also, as another example to mitigate or avoid read disturb conditions inthe PFET write port memory bit cell 502 in FIG. 6A, a read-assistcircuit employing a positive supply rail positive boost circuit can beemployed. The positive supply rail positive boost circuit is configuredto weaken a pull-down NFET in one or more inverters in a storage circuit501 of the PFET write port memory bit cell 502 in response to a readoperation (block 606C in FIG. 6B). Examples of memory systems thatinclude read-assist circuits employing a positive supply rail positiveboost circuit for a PFET write port memory bit cell are shown in FIG. 12discussed below.

As discussed above, to mitigate or avoid read disturb conditions in thePFET read port memory bit cell 502 in FIG. 6A, the PFET accesstransistors 528(0), 528(1) can be weakened during read operations. Inthis manner, the wrong voltage (e.g., GND voltage) is not driven fromthe pre-discharged bitline 114 and the complement bitline 114′ into thetrue storage node 522 and complement storage node 522′, respectively. Inthis regard, FIG. 7 illustrates an exemplary wordline driver 508A thatincludes a read-assist circuit 700 in the form of a wordline positiveboost circuit 702. The wordline positive boost circuit 702 in thisexample is configured to positively boost the voltage on the wordline(WL) 506 to weaken the PFET access transistors 528(0), 528(1) inresponse to a read operation to mitigate or avoid a read disturbcondition from occurring. In this manner, the PFET access transistors528(0) or 528(1) do not drive the voltages from the bitline 114 or thecomplement bitline 114′ into the true storage node 522 or complementstorage node 522′, respectively, in response to a read operation, thuscausing a read disturb condition. By boosting the voltage on thewordline (WL) 506, the drive current I_(D) (i.e., drive strength) of thePFET access transistors 528(0), 528(1) is weakened according to thefollowing saturation drive current equation by decreasing gate (G)voltage-to-source (S) voltage (Vgs), as follows:

I _(D)=½μC _(ox) W/L(V _(GS) −V _(TH))²

where:

-   -   I_(D) is drive current,    -   ‘μ’ is the charge carrier effective mobility,    -   ‘W’ is the gate width,    -   ‘L’ is the gate length,    -   ‘C_(ox)’ is the capacitance of the oxide layer;    -   ‘V_(GS)’ is the gate to source Voltage, and    -   ‘V_(TH)’ is the threshold voltage.

With reference to FIG. 7, to perform a read or write operation in thememory bit cell 502 in FIG. 7, the wordline (WL) 506 must be driven to alogical ‘0’ to turn on the PFET access transistors 528(0), 528(1) in thememory bit cell 502. In a read operation, the wordline (WL) 506 isdriven to a logical ‘0’ after the bitline 514 and the complement bitline514′ are pre-discharged. In this regard, the wordline driver 508A inFIG. 7 includes a discharge control circuit 703. The discharge controlcircuit 703 is coupled to the wordline (WL) 506. The discharge controlcircuit 703 is configured to receive a charge control signal 705 from acharge control circuit 707 as an input. As discussed in more detailbelow, the discharge control circuit 703 is configured to couple thewordline (WL) 506 to the ground node (GND) in response to the chargecontrol signal 705 indicating a charge disable state. However, as alsodiscussed in more detail below, the discharge control circuit 703 isalso configured to decouple the wordline (WL) 506 from the ground node(GND) to leave the wordline (WL) 506 in a floating state to allow aboost generator circuit 709 to positively boost the voltage on thewordline (WL) 506 in response to the charge control signal 705indicating a charge enable state. In this example, the discharge controlcircuit 703 includes an NFET 704. The NFET 704 is activated during awrite operation to drive the wordline (WL) 506 to a logical ‘0’ toactivate the PFET access transistors 528(0), 528(1) during a writeoperation, because the charge control signal 705 is based on the readclock signal 510 inverted by inverter 710 in the charge control circuit707. When a write operation is to be performed, a read enable signal 511transitions high to select the memory bit cell 502 for the writeoperation. An output 712 of an inverter 710 in the charge controlcircuit 707 activates the NFET 704 in the discharge control circuit 703to pass the GND voltage to the wordline (WL) 506. The NFET 704 passes astrong logical ‘0’ signal.

However, in response to a read operation, the NFET 704 in the dischargecontrol circuit 703 is shut off due to the inverter 708 inverting theread clock signal 510, which has transitioned from low to high, on theoutput 712, which has transitioned from high to low. This leaves thewordline (WL) 506 floating. The boost generator circuit 709 provided inthe wordline positive boost circuit 702 is activated based on the chargecontrol signal 705 and the read enable signal 511 in this exampleindicating a read operation, to positively boost the voltage of thewordline (WL) 506 to weaken the PFET access transistors 528(0), 528(1).

In this example, a PFET 714 is included in the boost generator circuit709. The gate (G) of the PFET 714, which is coupled to the output 712 ofthe inverter 710 in the charge control circuit 707, is activated inresponse to a read operation to boost the wordline (WL) 506. When theread enable signal 511 is a logical ‘1’, the PFET 714 in the boostgenerator circuit 709 passes a signal above GND voltage, between athreshold voltage (Vt) and GND voltage, to the wordline (WL) 506. Thisis because a PFET 714 passes a weak logical ‘0’ signal. Thus, instead ofthe wordline (WL) 506 being driving all the way down to the GND voltage(logical ‘0’) in a charge disable state based on the charge controlsignal 705 and read enable signal 511, the wordline (WL) 506 is drivento a voltage level between Vt and GND voltage. This has the effect ofweakening the PFET access transistors 528(0), 528(1) to provide aread-assist during read operations in the memory bit cell 502. Thus, thedrive strength of the PFETs 524(0), 524(1) in the inverters 520(0),520(1) (see FIG. 6A) in the memory bit cell 502 can overcome theweakened PFET access transistors 528(0), 528(1) in response to a readoperation to quickly re-charge any lost charge on a true storage node522 or complement storage node 522′ at a voltage of logical ‘1’, whichis to be coupled to the bitline 514 or complement bitline 514′.

FIG. 8 is another exemplary wordline driver 508B that includes aread-assist circuit 800 in the form of another example of a wordlinepositive boost circuit 802. Like the wordline positive boost circuit 702in FIG. 7, the wordline positive boost circuit 802 in FIG. 8 isconfigured to boost the wordline (WL) 506 in the memory bit cell 502 toweaken the PFET access transistors 528(0), 528(1) in response to a readoperation to mitigate or avoid a read disturb condition from occurring.In this manner, the PFET access transistors 528(0) or 528(1) do notdrive the voltages from the bitline 114 or the complement bitline 114′into the true storage node 522 or the complement storage node 522′,respectively, in response to a read operation, thus causing a readdisturb condition. Common elements between the wordline positive boostcircuit 802 in FIG. 8 and the wordline positive boost circuit 702 inFIG. 7 are shown with common element numbers, and thus will not bere-described.

With reference to FIG. 8, the wordline positive boost circuit 802 inthis example is configured to weakly turn on PFET access transistors528(0), 528(1) such that a read operation does not disturb the data 532and/or complement data 532′ stored in the storage circuit 501 of thePFET read port memory bit cell 502. In this regard, the gates (G) of thePFET access transistors 528(0), 528(1) are momentarily driven to logical‘0’ (e.g., GND). The gates (G) of the PFET access transistors 528(0),528(1) are then raised to a voltage higher than logical ‘0’ in responseto a read operation while still keeping the PFET access transistors528(0), 528(1) on or active, to avoid or mitigate a read disturbcondition.

In this regard, with continued reference to FIG. 8, while the read clocksignal 510 is at logical ‘0’, and the read enable signal 511 is drivento logical ‘1’, the inverter 708 in the discharge control circuit 703drives the wordline (WL) 506 to logical ‘0.’ This activates or turns onthe PFET access transistors 528(0), 528(1) outside of a read operation.An output 804 of the charge control circuit 807 is driven to logical ‘1’by the read clock signal 510 being logical ‘0 and the read enable signal511, which generates a charge control signal 805. The charge controlsignal 805 being a logical ‘1’ activates or turns on the NFET 704 in thedischarge control circuit 703. This causes the wordline (WL) 506 to bedriven to ground (GND) voltage through the NFET 704 in the chargecontrol circuit 807 outside of a read operation. Also, the chargecontrol signal 805 being logical ‘1’ causes a boost generator circuit809 in the wordline positive boost circuit 802 to not be activated tocouple a positive charge onto the wordline (WL) 506 to boost the voltageof the wordline (WL) 506 in response to the read operation.

However, once the read clock signal 510 is driven to logical ‘1,”meaning that a read operation is enabled, the output 804 of a NAND gate806 in the charge control circuit 807 is driven to logical ‘0.’ Thisdisables the NFET 704 in the discharge control circuit 703, which causesthe wordline (WL) 506 to float and not be driven to ground (GND) voltagethrough the NFET 704. Also in response to the read operation, the output804 in the charge control circuit 807 is driven to logical ‘0” to alsodrive the charge control signal 805 to logical ‘0.’ The charge controlsignal 805 being logical ‘0’ causes the boost generator circuit 809 inthe wordline positive boost circuit 802 to be activated to couple apositive charge onto the wordline (WL) 506 to boost the voltage of thewordline (WL) 506 in response to the read operation, and thus weaken thePFET access transistors 528(0), 528(1).

In this example, the boost generator circuit 809 includes a plurality ofcharge generating circuits 808(0)-808(X) provided in the form of NORgates. The charge generating circuits 808(0)-808(X) are enabled byprogrammable charge signals b(0)-b(X), respectively, such that theamount of charge generated by the boost generator circuit 809 isproportionally programmable. In response to the charge generatingcircuits 808(0)-808(X) being enabled, the voltage of the wordline (WL)506 will be positively boosted by a voltage proportional to the numberand the value of respective charge storage circuits 810(0)-810(X) in acharge storage unit 811 that are programmed to couple onto the wordline(WL) 506. In this example, the charge storage circuits 810(0)-810(X) arecomprised of capacitors.

FIG. 9 is another exemplary wordline driver 508C that includes aread-assist circuit 900 in the form of a wordline positive boost circuit902. The wordline positive boost circuit 902 is similar to the wordlinepositive boost circuit 702 in FIG. 7, except that the wordline boostcircuit 902 in FIG. 9 allows a different voltage (Vdd/X) other than thevoltage (Vdd) powering the inverter 708 in FIG. 9 to be driven onto thewordline (WL) 506 to boost the voltage of the wordline (WL) 506. Commoncomponents in the wordline driver 508C between FIG. 7 and FIG. 9 areshown with common element numbers, and thus will not be re-described.

With reference to FIG. 9, in response to a read operation, as previouslydiscussed, the NFET 704 in the discharge control circuit 703 is turnedoff due to the inverter 710 in the charge control circuit 907 invertingthe read clock signal 510 on the output 712. This leaves the wordline(WL) 506 floating. The gate (G) of an NFET 906 provided in a boostgenerator circuit 909 receives a signal based on the read enable signal511 from the output 913 of the inverter 908 in a charge control circuit907. In this manner, the NFET 906 is not activated in response to a readoperation such that the voltage Vdd is not provided to the wordline (WL)506 to boost the wordline (WL) 506 to voltage (Vdd). Instead, to allowfor the option to boost the voltage of the wordline (WL) 506 based on avoltage other than voltage (Vdd), such as voltage Vdd/X, the boostgenerator circuit 909 also includes a PFET 910 to provide voltage Vdd/Xto another PFET 912 in this example. The PFET 910 is activated based onan output 913 of the inverter 908 in response to a read operation (i.e.,the read enable signal 511) such that voltage Vdd/X is provided to thePFET 912 in response to a read operation. The PFET 912 behaves like thePFET 714 in the boost generator circuit 709 in FIG. 7 to boost thevoltage of the wordline (WL) 506 in response to a read operation, exceptthat the PFET 912 in the boost generator circuit 909 in FIG. 9 can boostthe voltage wordline (WL) 506 based on a different voltage supplyproviding voltage Vdd/X in this example.

FIG. 10 is another exemplary wordline driver 508D that is configured topositively boost the wordline (WL) 506 to a voltage other than voltageVdd in response to a read operation. In this regard, the wordline driver508D includes a read-assist circuit 1000 in the form of another exampleof a wordline positive boost circuit 1002. The wordline positive boostcircuit 1002 is similar to the wordline positive boost circuit 702 inFIG. 7 and the wordline boost circuit 902 in FIG. 9. Common componentsin the wordline driver 508D between FIG. 10 and the wordline driver 508Aand 508C in FIGS. 7 and 9 are shown with common element numbers in FIG.10, and thus will not be re-described. A boost generator circuit 1009provided in the wordline positive boost circuit 1002 in FIG. 10 includesan NFET 906 like included in the boost generator circuit 909 in FIG. 9.However, in the boost generator circuit 1009 in FIG. 10, instead of theNFET 906 being sourced to ground GND, the NFET 906 is sourced to voltageVdd/X. The NFET 906 is activated based on the read clock signal 510,which causes the charge control circuit 707 to generate the output 712to cause the inverter 908 to activate the NFET 906 in response to a readoperation. In response to the read operation, the NFET 906 couplesvoltage Vdd/X to the wordline (WL) 506 to boost the wordline (WL) 506 tovoltage Vdd/X, which may be a fraction of voltage (Vdd).

The wordline positive boost circuits 702, 802, 902, and 1002 in FIGS.7-10 all are capable of providing a voltage boost to the wordline (WL)506 of the memory bit cell 502 during read operations to mitigate oravoid read disturb conditions in the memory bit cell 502. It is alsopossible to boost the bitline 514 and complement bitline 514′ in thememory bit cell 502, instead of boosting the wordline (WL) 506, tomitigate or avoid read disturb conditions in the memory bit cell 502that employs the PFET read ports through the PFET access transistors528(0), 528(1). Boosting the bitline 514 and the complement bitline 514′in the memory bit cell 502 in response to a read operation can reducethe gate (G) voltage-to-source (S) voltage (Vgs) of the PFET accesstransistors 528(0), 528(1), and thus weakens the PFET access transistors528(0), 528(1). This is opposed to a full voltage Vdd voltage beingprovided across a PFET access transistor 528(0) or 528(1) when a logical‘1’ is stored at a respective true storage node 522 or complementstorage node 522′. It is also possible to boost the bitline 514 andcomplement bitline 514′ in lieu of or in combination with boosting thewordline (WL) 506 to weaken the PFET access transistors 528(0), 528(1)during read operations to mitigate or avoid read disturb conditions.

In this regard, FIG. 11 is a circuit diagram of the sense amplifier 516,a read-assist circuit 1100 in the form of a bitline positive boostcircuit 1102 and a PFET read port memory bit cell 502 of the SRAM system500 in FIG. 5. In this example, the bitline positive boost circuit 1102is provided in a bitline driver 512 for a bit cell column M of the PFETread port memory bit cell 502. The bitline positive boost circuit 1102is configured to boost voltage on the bitline 514 and complement bitline514′ in response to a read operation for the memory bit cell 502 toweaken the respective PFET access transistors 528(0), 528(1). In thisregard, the memory bit cell 502 is provided just as illustrated in FIG.6A, and thus will not be re-described.

With reference to FIG. 11, when performing a read operation on thememory bit cell 502, the bitline 514 and the complement bitline 514′ arepre-discharged before the wordline (WL) 506 is asserted, as previouslydescribed above. However, in the memory bit cell 502 in FIG. 6A and asshown in FIG. 11, the bitline 514 and the complement bitline 514′ werepre-discharged to GND voltage. However, in this example in FIG. 11, thebitline positive boost circuit 1102 in this example includes PFETs1004(0), 1004(1). This is opposed to, for example, providing NFETs forpre-discharging the bitline 514 and the complement bitline 514′. ThePFETs 1004(0), 1004(1) in the bitline positive boost circuit 1102 areconfigured to pre-discharge the bitline 514 and the complement bitline514′, respectively, to the threshold voltage (Vt) of the PFETs 1004(0),1004(1) in response to a pre-discharge enable 1106. The PFETs 1004(0),1004(1) do not pass a strong logical ‘0’ voltage. Thus, the bitline 514and the complement bitline 514′ are positively boosted to the thresholdvoltage (Vt) of the respective PFETs 1004(0), 1004(1) above GND duringthe pre-discharge stage. Subsequently, when the wordline (WL) 506 isasserted to read the memory bit cell 502 in response to a readoperation, the gate (G) voltage-to-source (S) voltage (Vgs) of the PFETaccess transistor 528(0) or 528(1) is Vdd−Vt (i.e., Vdd voltage minusthe threshold voltage (Vt) of the respective PFETs 1004(0), 1004(1)),which weakens the PFET access transistors 528(0), 528(1). This mitigatesor avoids a read disturb condition that can occur when the true storagenode 522 or the complement storage node 522′ has a logical ‘1’ voltagestored, as previously discussed above with regard to FIG. 6A.

It is also possible to increase the drive strength of the PFETs 524(0),524(1) in the memory bit cell 502 in FIG. 6A, instead of or in additionto boosting the wordline (WL) 506 and/or boosting the bitline 514 andcomplement bitline 514′ in the memory bit cell 502, to mitigate or avoidread disturb conditions in the memory bit cell 502. Boosting the pull-upPFETs 524(0), 524(1) in the memory bit cell 502 in response to a readoperation allows the pull-up PFETs 524(0), 524(1) to quickly re-chargeany lost charge on the true storage node 522 or the complement storagenode 522′ as the voltage at the true storage node 522 is coupled to thebitline 514. Thus, any loss of charge due to charge sharing at the truestorage node 522 or the complement storage node 522′ is mitigated andcan cause the respective inverters 520(0) or 520(1) to flip the voltageVdd on the complement storage node 522′ or the true storage node 522,respectively, from a logic ‘0’ to a logic ‘1’.

In this regard, FIG. 12 illustrates an exemplary read-assist circuit1200 in the form of a positive supply rail positive boost circuit 1202.The positive supply rail positive boost circuit 1202 is configured toboost the voltage of a positive supply rail 1203 of the PFET read portmemory bit cell 502 that receives a supply voltage (Vdd) coupled to thepull-up PFETs 524(0), 524(1) of the cross-coupled inverters 520(0),520(1) (see also, FIG. 5). In this regard, the positive supply railpositive boost circuit 1202is configured to boost the voltage suppliedto the pull-up PFETs 524(0), 524(1) to cause the pull-up PFETs 524(0),524(1) to be stronger than the PFET access transistors 528(0), 528(1) inthe memory bit cell 502 in response to a read operation to mitigate oravoid a read disturb condition. As discussed below, the positive supplyrail positive boost circuit 1202 is configured to couple the pull-upPFETs 524(0), 524(1) to a higher voltage than voltage (Vdd) in thisexample.

In this regard, with reference to FIG. 12, when a read operation occursaccording to the transition of the read clock signal 510 provided as acharge control signal 1205 to a higher voltage level, the read clocksignal 510 is provided as an input to a boost generator circuit 1209. Inthis example, the boost generator circuit 1209 is comprised of aplurality of charge generating circuits 1204(0)-1204(Y) provided in theform of AND gates. The charge generating circuits 1204(0)-1204(Y) alsohave respective programmable charge lines 1206(0)-1206(Y) that can beprogrammed to allow any number of the charge generating circuits1204(0)-1204(Y) desired to charge respective charge storage circuits1208(0)-1208(Y) provided in a charge storage unit 1211 in this example.The charge storage circuits 1208(0)-1208(Y) are capacitors in thisexample. During the read operation, the charge stored in the chargestorage circuits 1208(0)-1208(Y) is coupled to an output 1210 of thecharge storage unit 1211, which is coupled to the positive supply rail1203 and to the pull-up PFETs 524(0), 524(1). In this manner, the chargedischarged from the charge storage unit 1211 to the positive supply rail1203 boosts the voltage coupled to the pull-up PFETs 524(0), 524(1)above voltage (Vdd), thus strengthening the PFETs 524(0), 524(1) and thecross-coupled inverters 520(0), 520(1). During a write operation, thecharge generating circuits 1204(0)-1204(Y) are not driving the output1210 coupled to the positive supply rail 1203, and thus the output 1210is left floating such that only voltage (Vdd) is coupled to the pull-upPFETs 524(0), 524(1) in the inverters 520(0), 520(1) for normal writeoperations.

The read-assist circuits for memory bit cells employing a PFET readport(s) disclosed herein to mitigate or avoid read disturb conditionsfor the PFET read port memory bit cells according to aspects disclosedherein, may be provided in or integrated into a memory in anyprocessor-based device. Examples, without limitation, include a set topbox, an entertainment unit, a navigation device, a communicationsdevice, a fixed location data unit, a mobile location data unit, amobile phone, a cellular phone, a computer, a portable computer, adesktop computer, a personal digital assistant (PDA), a monitor, acomputer monitor, a television, a tuner, a radio, a satellite radio, amusic player, a digital music player, a portable music player, a digitalvideo player, a video player, a digital video disc (DVD) player, and aportable digital video player.

In this regard, FIG. 13 illustrates an example of a processor-basedsystem 1300. Any component or circuit of the processor-based system 1300can employ PFET read port memory bit cells employing read-assistcircuits disclosed herein to mitigate or avoid read disturb conditionsfor the PFET read port memory bit cells according to aspects disclosedherein. In this example, the processor-based system 1300 includes one ormore central processing units (CPUs) 1302, each including one or moreprocessors 1304. The CPU(s) 1302 may have cache memory 1306 coupled tothe processor(s) 1304 for rapid access to temporarily stored data. As anexample, the cache memory 1306 can employ PFET read port memory bitcells 1308, including the PFET read port memory bit cell 502 illustratedin FIG. 5. The CPU(s) 1302 is coupled to a system bus 1310 and canintercouple master and slave devices included in the processor-basedsystem 1300. As is well known, the CPU(s) 1302 communicates with theseother devices by exchanging address, control, and data information overthe system bus 1310. For example, the CPU(s) 1302 can communicate bustransaction requests to a memory controller 1312 in a memory system 1314as an example of a slave device. Although not illustrated in FIG. 13,multiple system buses 1310 could be provided, wherein each system bus1310 constitutes a different fabric. In this example, the memorycontroller 1312 is configured to provide memory access requests to amemory array 1316 in the memory system 1314. As an example, the memoryarray 1316 can also include PFET read port memory bit cells 1308 thatinclude read-assist circuits.

Other devices can be connected to the system bus 1310. As illustrated inFIG. 13, these devices can include the memory system 1314, one or moreinput devices 1320, one or more output devices 1322, one or more networkinterface devices 1324, and one or more display controllers 1326, asexamples. The input device(s) 1320 can include any type of input device,including but not limited to input keys, switches, voice processors,etc. The output device(s) 1322 can include any type of output device,including but not limited to audio, video, other visual indicators, etc.The network interface device(s) 1324 can be any devices configured toallow exchange of data to and from a network 1328. The network 1328 canbe any type of network, including but not limited to a wired or wirelessnetwork, a private or public network, a local area network (LAN), a widelocal area network (WLAN), and the Internet. The network interfacedevice(s) 1324 can be configured to support any type of communicationsprotocol desired.

The CPU(s) 1302 may also be configured to access the displaycontroller(s) 1326 over the system bus 1310 to control information sentto one or more displays 1330. The display controller(s) 1326 sendsinformation to the display(s) 1330 to be displayed via one or more videoprocessors 1332, which process the information to be displayed into aformat suitable for the display(s) 1330. The display(s) 1330 can includeany type of display, including but not limited to a cathode ray tube(CRT), a liquid crystal display (LCD), a plasma display, etc.

A non-transitory computer-readable medium, such as the memory system1314 in FIG. 13 as a non-limiting example, may also have stored thereoncomputer executable instructions which, when executed, cause the CPU(s)1302 to store a library cell 1334 for an integrated circuit (IC) design.The library cell 1334 may be part of a cell library. The library cell1334 comprises a library memory bit cell 1336, which may be a librarycell based on the design of any PFET read port memory bit cellsdiscussed herein. As discussed above, the PFET read port memory bitcells comprise a storage circuit configured to store data. The PFET readport memory bit cells also comprise one or more PFET access transistorscoupled to the storage circuit. Each of the one or more PFET accesstransistors comprises a gate configured to be activated by a wordline inresponse to a read operation to cause the one or more PFET accesstransistors to pass the data from the storage circuit to a bitlineread-assist circuit coupled to the library memory bit cell 1336. Thelibrary cell 1334 may also comprise a read-assist circuit configured toboost a voltage in the library memory bit cell 1336 in response to theread operation to assist in transferring the data from the storagecircuit to a bitline.

Note that the use of PFET and NFET in this disclosure can includePMOSFETs and NMOSFETs that are metal oxide semiconductors (MOSs). ThePFETs and NFETs discussed herein can include other types of oxide layersother than metal. Also note that any of the assist circuits disclosedherein can be provided for either or both of the bitline and complementbitline of the memory bit cells disclosed herein.

Those of skill in the art will further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithms describedin connection with the aspects disclosed herein may be implemented aselectronic hardware, instructions stored in memory or in anothercomputer-readable medium and executed by a processor or other processingdevice, or combinations of both. The master and slave devices describedherein may be employed in any circuit, hardware component, integratedcircuit (IC), or IC chip, as examples. Memory disclosed herein may beany type and size of memory and may be configured to store any type ofinformation desired. To clearly illustrate this interchangeability,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality. Howsuch functionality is implemented depends upon the particularapplication, design choices, and/or design constraints imposed on theoverall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implemented orperformed with a processor, a Digital Signal Processor (DSP), anApplication Specific Integrated Circuit (ASIC), a Field ProgrammableGate Array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. A processormay be a microprocessor, but in the alternative, the processor may beany conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

It is also noted that the operational steps described in any of theexemplary aspects herein are described to provide examples anddiscussion. The operations described may be performed in numerousdifferent sequences other than the illustrated sequences. Furthermore,operations described in a single operational step may actually beperformed in a number of different steps. Additionally, one or moreoperational steps discussed in the exemplary aspects may be combined. Itis to be understood that the operational steps illustrated in the flowchart diagrams may be subject to numerous different modifications aswill be readily apparent to one of skill in the art. Those of skill inthe art will also understand that information and signals may berepresented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein, but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A memory system, comprising: a memory bit cell,comprising: a storage circuit configured to store data and comprising: apositive supply rail; a negative supply rail; and one or more inverterseach comprising a pull-up P-type field-effect transistor (FET) (PFET)coupled to a pull-down N-type FET (NFET), wherein each pull-up PFET ofthe one or more inverters is coupled to the positive supply rail, andeach pull-down NFET of the one or more inverters is coupled to thenegative supply rail; and one or more PFET access transistors coupled tothe storage circuit; and each of the one or more PFET access transistorscomprising a gate configured to be activated by a wordline in responseto a read operation to cause the one or more PFET access transistors topass the data from the storage circuit to a bitline read-assist circuitcoupled to the memory bit cell; and a read-assist circuit configured toboost a voltage in the memory bit cell in response to the read operationto assist in transferring the data from the storage circuit to abitline, the read-assist circuit comprising a positive supply railpositive boost circuit coupled to the positive supply rail of at leastone inverter among the one or more inverters, the positive supply railpositive boost circuit configured to positively boost a voltage on thepositive supply rail to strengthen the one or more inverters in thestorage circuit in response to the read operation.
 2. The memory systemof claim 1, wherein the one or more PFET access transistors comprises: afirst PFET access transistor coupled to the storage circuit, the firstPFET access transistor comprising a first gate configured to beactivated by the wordline in response to the read operation to cause thefirst PFET access transistor to pass the data from the storage circuitto the bitline; and a second complement PFET access transistor coupledto the storage circuit, the second complement PFET access transistorcomprising a second gate configured to be activated by the wordline inresponse to the read operation to cause the second complement PFETaccess transistor to pass complement data complementary to the data fromthe storage circuit to a complement bitline.
 3. The memory system ofclaim 2, wherein: the storage circuit is comprised of a storage node anda complement storage node; the first PFET access transistor isconfigured to pass the data from the storage node to the bitline inresponse to activation of the wordline for the read operation; and thesecond complement PFET access transistor is configured to pass thecomplement data from the complement storage node to the complementbitline in response to activation of the wordline for the readoperation.
 4. The memory system of claim 1, wherein: the positive supplyrail positive boost circuit is configured to positively boost thevoltage on the positive supply rail above a voltage supply coupled tothe positive supply rail to strengthen the one or more inverters in thestorage circuit in response to the read operation.
 5. The memory systemof claim 1, wherein the positive supply rail positive boost circuit isconfigured to positively charge the voltage on the positive supply railin response to a charge control signal indicating a charge enable state.6. The memory system of claim 1, wherein the positive supply railpositive boost circuit comprises a boost generator circuit and a chargestorage unit coupled to the boost generator circuit and the positivesupply rail; the charge storage unit is configured to store a charge;and the boost generator circuit is configured to: generate a charge tobe stored in the charge storage unit outside of the read operation; andcouple the charge stored in the charge storage unit onto the positivesupply rail to positively boost the voltage on the positive supply railin response to the read operation.
 7. The memory system of claim 6,wherein the boost generator circuit is comprised of a plurality ofprogrammable charge generating circuits each configured to selectivelycontribute to the charge stored in the charge storage unit in responseto a respective programmable charge signal.
 8. The memory system ofclaim 1, comprising: a plurality of memory bit cells each configured tostore voltage data in response to a write operation, each memory bitcell among the plurality of memory bit cells comprising one or more PFETaccess transistors each comprising a gate configured to be activated bythe wordline in response to the read operation; and the read-assistcircuit configured to positively boost a voltage in the plurality ofmemory bit cells in response to the read operation to assist intransferring the data from the storage circuit to the bitline.
 9. Thememory system of claim 8, wherein the plurality of memory bit cells aredisposed in a memory bit cell row of a memory array.
 10. The memorysystem of claim 1 provided in a processor-based system.
 11. A method ofreading data from a memory bit cell, comprising: pre-discharging atleast one bitline coupled to an access node of one or more P-typefield-effect transistor (FET) (PFET) access transistors in a memory bitcell in response to a read operation; activating a wordline coupled to agate of the one or more PFET access transistors in response to the readoperation to transfer data from a storage circuit to the access node andthe at least one bitline; and boosting a voltage in the memory bit cellin response to the read operation to assist in transferring the datafrom the storage circuit to the access node; wherein: the storagecircuit further comprises a positive supply rail, a negative supplyrail, and one or more inverters comprising a pull-up PFET and apull-down N-type FET (NFET); each pull-up PFET of the one or moreinverters is coupled to the positive supply rail, and each pull-downNFET of the one or more inverters is coupled to the negative supplyrail; and boosting the voltage comprises positively boosting a voltageon the positive supply rail to strengthen the one or more inverters inthe storage circuit in response to the read operation.
 12. The method ofclaim 11, wherein: pre-discharging the at least one bitline comprises:pre-discharging a bitline coupled to a first access node of a first PFETaccess transistor in the memory bit cell in response to the readoperation; and pre-discharging a complement bitline coupled to a secondaccess node of a second complement PFET access transistor in the memorybit cell in response to the read operation; activating the wordlinecomprises: activating the wordline coupled to a gate of the first PFETaccess transistor in response to the read operation to transfer firstdata from the storage circuit to the first access node to the bitline;and activating the wordline coupled to a gate of the second complementPFET access transistor in response to the read operation to transfersecond data from the storage circuit to the second access node to thecomplement bitline; and boosting the voltage further comprises boostingthe voltage in the memory bit cell in response to the read operation toassist transferring the first data from the storage circuit to the firstaccess node and transferring the second data from the storage circuit tothe second access node.
 13. The method of claim 11, wherein positivelyboosting the voltage further comprises positively boosting the voltageon the positive supply rail above a voltage supply coupled to thepositive supply rail to strengthen the one or more inverters in thestorage circuit in response to the read operation.
 14. The method ofclaim 11, wherein positively boosting the voltage further comprisespositively charging the voltage on the positive supply rail in responseto a charge control signal indicating a charge enable state.
 15. Themethod of claim 11, further comprising: storing a charge in a chargestorage unit coupled to the positive supply rail; generating a charge tobe stored in the charge storage unit outside of the read operation; andcoupling the charge stored in the charge storage unit onto the wordlineto positively boost the voltage on the wordline in response to the readoperation.
 16. The method of claim 15, further comprising selectivelycontrolling an amount of the charge stored in the charge storage unit inresponse to a respective programmable charge signal.
 17. A memorysystem, comprising: a memory bit cell, comprising: a storage circuitconfigured to store data; one or more P-type field-effect transistor(FET) (PFET) access transistors coupled to the storage circuit; and eachof the one or more PFET access transistors comprising a gate configuredto be activated by a wordline in response to a read operation to causethe one or more PFET access transistors to pass the data from thestorage circuit to a bitline read-assist circuit coupled to the memorybit cell; and a read-assist circuit configured to boost a voltage in thememory bit cell in response to the read operation to assist intransferring the data from the storage circuit to a bitline, wherein theread-assist circuit comprises a bitline positive boost circuit coupledto the bitline, the bitline positive boost circuit configured topositively boost a voltage on the bitline to positively boost a gate (G)voltage-to-source (S) voltage (Vgs) of the one or more PFET accesstransistors in response to the read operation.
 18. The memory system ofclaim 17, wherein the bitline positive boost circuit is configured topositively boost the voltage on the bitline in response to apre-discharge enable signal indicating the read operation.
 19. Thememory system of claim 17, wherein the bitline positive boost circuit isprovided in a bitline driver configured to pre-discharge bitlines for aplurality of memory bit cells.
 20. The memory system of claim 17,wherein the bitline positive boost circuit comprises at least one PFETconfigured to pre-discharge the bitline to a threshold voltage of the atleast one PFET to positively boost the gate (G) voltage-to-source (S)voltage (Vgs) of the one or more PFET access transistors in response tothe read operation.
 21. The memory system of claim 17, wherein: thestorage circuit further comprises one or more inverters each comprisinga pull-up PFET coupled to a pull-down N-type FET (NFET).
 22. The memorysystem of claim 17, wherein the one or more PFET access transistorscomprises: a first PFET access transistor coupled to the storagecircuit, the first PFET access transistor comprising a first gateconfigured to be activated by the wordline in response to the readoperation to cause the first PFET access transistor to pass the datafrom the storage circuit to the bitline; and a second complement PFETaccess transistor coupled to the storage circuit, the second complementPFET access transistor comprising a second gate configured to beactivated by the wordline in response to the read operation to cause thesecond complement PFET access transistor to pass complement datacomplementary to the data from the storage circuit to a complementbitline.
 23. The memory system of claim 22, wherein the read-assistcircuit comprises a bitline positive boost circuit coupled to thebitline and the complement bitline, the bitline positive boost circuitconfigured to positively boost a voltage on the bitline and thecomplement bitline to positively boost a gate (G) voltage-to-source (S)voltage (Vgs) of the first PFET access transistor and the secondcomplement PFET access transistor in response to the read operation. 24.The memory system of claim 22, wherein: the storage circuit is comprisedof a storage node and a complement storage node; the first PFET accesstransistor is configured to pass the data from the storage node to thebitline in response to activation of the wordline for the readoperation; and the second complement PFET access transistor isconfigured to pass the complement data from the complement storage nodeto the complement bitline in response to activation of the wordline forthe read operation.
 25. The memory system of claim 17, comprising: aplurality of memory bit cells each configured to store voltage data inresponse to a write operation, each memory bit cell among the pluralityof memory bit cells comprising one or more PFET access transistors eachcomprising a gate configured to be activated by the wordline in responseto the read operation; and the read-assist circuit configured topositively boost a voltage in the plurality of memory bit cells inresponse to the read operation to assist in transferring the data fromthe storage circuit to the bitline.
 26. The memory system of claim 25,wherein the plurality of memory bit cells are disposed in a memory bitcell row of a memory array.
 27. A method of reading data from a memorybit cell, comprising: pre-discharging at least one bitline coupled to anaccess node of one or more P-type field-effect transistor (FET) (PFET)access transistors in a memory bit cell in response to a read operation;activating a wordline coupled to a gate of the one or more PFET accesstransistors in response to the read operation to transfer data from astorage circuit to the access node and the at least one bitline; andboosting a voltage in the memory bit cell in response to the readoperation to assist in transferring the data from the storage circuit tothe access node, wherein boosting the voltage comprises positivelyboosting a voltage on the at least one bitline.
 28. The method of claim27, wherein: pre-discharging the at least one bitline comprises:pre-discharging a bitline coupled to a first access node of a first PFETaccess transistor in the memory bit cell in response to the readoperation; and pre-discharging a complement bitline coupled to a secondaccess node of a second complement PFET access transistor in the memorybit cell in response to the read operation; activating the wordlinecomprises: activating the wordline coupled to a gate of the first PFETaccess transistor in response to the read operation to transfer firstdata from the storage circuit to the first access node to the bitline;and activating the wordline coupled to a gate of the second complementPFET access transistor in response to the read operation to transfersecond data from the storage circuit to the second access node to thecomplement bitline; and boosting the voltage comprises boosting thevoltage in the memory bit cell in response to the read operation toassist transferring the first data from the storage circuit to the firstaccess node and transferring the second data from the storage circuit tothe second access node.
 29. The method of claim 27, wherein boosting thevoltage further comprises positively boosting a voltage on the at leastone bitline to positively boost a gate (G) voltage-to-source (S) voltage(Vgs) of the one or more PFET access transistors in response to the readoperation.
 30. The method of claim 27, wherein boosting the voltagefurther comprises positively boosting the voltage on the at least onebitline in response to a pre-discharge enable signal indicating the readoperation.